1. Field of the Invention
This invention relates to a hydrostatic hub drive with an integrated axial piston machine employing a swashplate design, in particular a wheel hub drive, with a stationary hub carrier in the form of a machine housing of the axial piston machine, a hub formed by a machine shaft and mounted inside the hub carrier so that it can rotate, and a hub bearing in the form of a shaft bearing.
2. Technical Considerations
A hub drive is described in DE 196 42 021 A1. This document describes two synchronously rotating cylinder blocks that are at an axial distance from each other. Each cylinder block contains a group of concentric cylinder bores, between which and at an angle to the axis of rotation of the axial piston machine that is in the form of a wheel motor, there is a non-rotating swashplate in the shape of a circular ring. Pistons that move longitudinally in the cylinder bores and are configured so that they displace hydraulic fluid on both ends of the pistons are supported against the pivotably mounted swashplate. These pistons each consist of two piston segments that have the same diameter, are at a distance from each other, are coaxial in relation to each other, are inserted in cylinder bores opposite one another, and are connected to each other by a bridge segment.
An object of this invention is to provide a hydrostatic hub drive of the general type described above but which is easier and more economical to manufacture and assemble than comparable known devices.
In a hub drive of the invention, the axial piston machine is configured as an individual drive unit having an individual cylinder block on a machine shaft that projects out of a machine housing through an outlet opening. A swashplate is located in an area close to or adjacent the outlet opening and a control base receptacle is located in an area farther from the outlet opening than is the swashplate. The hub drive of the invention thereby has only a few individual parts, all of which are easy to manufacture and assemble.
In one advantageous configuration of the invention, the axial piston motor is a fixed displacement motor and the swashplate is shaped into the machine housing. This arrangement minimizes the manufacturing cost for the above mentioned parts, because they are designed as one piece.
In another appropriate refinement of the invention, the swashplate is installed and oriented so that under operating conditions the radial components of the propulsion forces are effectively or substantially directed opposite to the external forces that are exerted on the hub bearing system. The load on the hub bearing system is thereby relieved, which contributes to an extended useful life.
In terms of assembly and installation, it is advantageous if a cover that is configured as a control base receptacle is detachably fastened to the machine housing.
In one advantageous embodiment of the hub drive of the invention, a brake is located radially between the cylinder block and the machine housing.
In one advantageous variant, it is also possible to locate a brake that is effectively or operationally connected with the machine shaft in a recess of the cover. The brake is thereby easier to access (to perform maintenance, for example). When the hub drive is installed, all that is necessary to access the brake is simply to remove the cover.
In this context it is appropriate if the brake has a spring-loaded brake piston which can be mechanically fixed in position against the action of the spring force on a spring abutment. Such a spring-loaded brake can be removed easily and without any danger of accidents when the brake piston is locked in position. This configuration also makes it possible to tow a vehicle that is equipped with the hub drive of the invention, if the brakes of the vehicle are closed and cannot be opened by the operating pressure, by mechanically releasing the brakes.
If the brake is in the form of a wet-running, spring-loaded, multiple-disc brake, advantages are achieved with regard to high performance and efficient utilization of the available space.
It is also advantageous if the machine housing has means for fastening the hub drive, wherein the cover can be removed even when the hub drive is fastened to the housing. It is thereby possible, for example, to perform maintenance activities on the brake without detaching the hub carrier.
To reduce the number of components, it is advantageous if a wheel flange that is designed to hold at least one wheel rim is shaped onto the machine shaft. This measure reduces the time, effort and expense of assembly. In this context, configurations are also possible in which the wheel flange has a rim centering device and concentric threaded borings.